Settling pond separation using permeable fabric and weighting

ABSTRACT

Liquids can be separated from the solids contained in slurries, sludges, etc. by forcing a liquid-permeable fabric, downward into the slurry so that solid materials are retained below said liquid-permeable fabric and liquids can be pumped or drained from above said liquid-permeable fabric. Apparatus is provided, comprising liquid-permeable fabrics and weighting means.

This is a continuation of application Ser. No. 601,121, filed Apr. 16,1984, now abandoned, which is a continuation of application Ser. No.382,273, filed May 26, 1982, now abandoned.

This invention concerns separation of liquids from solid materials usingfabrics.

BACKGROUND OF THE INVENTION

Filtration is a common means for extracting solids from liquids, usuallyinvolving forcing a slurry or mixture of solids and liquids throughfiltering materials. A slurry is usually taken to mean a waterysuspension or mixture of insoluble solids in a liquid. As used herein,the term will encompass mixtures or suspensions of solid materialscomprising particulate matter, gels, sludges and the like, which are atleast partially insoluble in a liquid component comprising water, liquidorganic or inorganic materials, and mixtures thereof. As used herein,such slurries can contain solids in suspension, or tending to settlenaturally with time. Normally the filtrate or liquid passes downwardthrough the filter with the solids remaining on the filter for recovery.

In many industries, e.g., the mining, oils and chemicals, wood pulp andagricultural industries, unfiltered waste slurries of liquids and solidsare impounded in dammed earthen areas or "settling ponds". A settlingpond is taken to be any concave depression in the ground, lined orunlined, which is used to collect slurries of solids and liquids.Generally such slurries are collected in settling ponds for separation,disposal or other processing. It is desirable to minimize the area ofthese settling ponds, to maximize disposal rates of slurries, andeventually to reclaim the areas by means including landfills and thelike. However, often these areas never dry nor solidify, sinceevaporation is slow, and the slurried or flocculated solids never settlesufficiently so that the liquids can be pumped off. Effective means fordewatering such settling ponds without removing the sediment or settledsolids are thus desirable. Similarly, it is desirable to have effectivemeans for separating the liquid from a contained slurry of solids andliquids in general.

SUMMARY OF THE INVENTION

It is an object of this invention to provide effective means forseparating the liquid from a contained slurry of solids and liquids. Itis another object of this invention to provide effective means forseparating the solids and liquids in settling ponds as described above.It is a further object to separate liquids from slurries of solids andliquids in settling ponds in a way such that the solids remain in thepond and the liquids are removed therefrom. It is a still further objectto remove liquids from the slurries in such ponds free from suspendedmaterial, undesired colors, etc. It is a further object to provide aprocess for separation of liquids from slurries of solids and liquids insuch a way that the filtering means utilized can be left in place atopthe separated solids as part of a landfill or other waste pile. It is afurther object to control the channels by which said liquids can beremoved from the slurry material when they are covered by filteringmeans. It is another object to provide a process for covering thefiltering means left in place atop separated solids with clay, earth,sand, aggregates, vegetable matter, or other materials to form part of alandfill. A still further object is to provide a method and apparatusfor the separation of liquids from slurries contained in vessels forindustrial or laboratory use.

In accordance with this invention, these and other objects can beaccomplished by placing a liquid-permeable fabric atop a containedslurry of solids and liquids, then causing it to sink such that thefabric effectively covers and confines the solids which were containedin the slurry, so that the liquid is filtered and separated above saidfabric. In one embodiment of the invention, the liquid can then beremoved by pumping, draining, decanting, evaporation or the like,leaving the separated and dewatered solids beneath said fabric. Thisprocess is distinct from conventional filtering methods, and from, e.g.,land-fill operations as described in GB Pat. No. 1,603,517, whereinhydraulic fill material is deposited in a water-filled cavity atopmultiple layers of "prefabricated consolidation blankets" to fill thecavity and displace the liquid therefrom.

In a preferred embodiment, the fabric of this invention is weighted by alayer of aggregate spread on its upper side, which also provides aporous channel through which the liquids can be drained or otherwiseextracted. For example, in one embodiment the liquid can be drained orpumped out by means placed in the aggregate layer, preferably perforatedtubes. Such a layer of aggregate can be covered with a second layer offabric and/or a layer of clay, thus forming a laminate. Liquids can thusbe separated from a contained slurry and removed without adding moreslurry or solids, and without significant spillage beyond thecontainment area, if desired. Examples of containment areas to whichthis invention is applicable include natural and artificial cavities ordepressions in the earth or masses of granular material, structuresresembling swimming pools or tanks, and industrial or laboratory vesselsof various sizes.

Methods and apparatus are thus provided for the separation of liquidsfrom a contained slurry of liquids and solids.

These and other objects, features and advantages of this invention willbe apparent to those skilled in the art from the following detaileddescription, the drawing, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a fragmental isometric view of a preferred embodiment of theinvention as applied to a settling pond.

FIG. 2 is a fragmental cross section of a portion of the preferredembodiment of the invention, as shown in FIG. 1.

FIG. 3 is a fragmental cross section of another preferred embodiment ofthe invention.

FIG. 4 is a fragmental cross section isometric view of the preferredembodiment of FIG. 2, with the addition of a common removal sumppositioned in the aggregate layer.

FIG. 5 is an isometric view of an embodiment of the invention whichpermits the removal of the fabric from the slurry surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment is discussed with reference to FIGS. 1 and 2.

In FIG. 1 an overall picture of a preferred embodiment of the inventionis given. A settling pond 1 with an earthen floor 2, which can have aliner (not shown) containing a slurry 30 composed of solids 4 andliquids 6, is being dewatered. Said slurry is covered with a sandwichcomprising non-woven fabric and aggregate generally shown by referencenumeral 8, said sandwich 8 being shown more clearly in FIG. 2, havingperforated tubes 10 extending through the aggregate layer thereof. Thenon-woven fabric layers merge along the edge 12 and extend a distancepast the edge 5 of the settling pond 1 to totally enclose the aggregatelayer 32. Along opposing sides 14 and 16 said merged fabric 12 andperforated tubes 10 are in fluid connection with a common manifold pipe18 for removing the filtered liquid. A non-permeable layer of clay 20 islaid over the sandwich 8, the manifold 18 and the settling pond 1, alsoextending a distance beyond the edge 5 of said pond 1, common manifoldpipe 18 and the non-woven merged fabric edge 12 to render the entiresystem essentially sealed from the external environment. This extensionof sealant also effectively contains all liquids and solids within thesystem. In operation the weight of the clay 20 and aggregate sandwich 8exert a downward force on the slurry of solids 4 and liquids 6, causingthe liquid 6 to filter through the non-woven fabric into the aggregatesection of the sandwich 8. Said liquid 6 is then removed by the wickingaction of the non-woven material and/or draining or pumping, using theperforated tubes 10, both being tied to a manifold 18 removal means forpurification, disposal or recycling. The pond 1 and clay cover layer 20are impervious to the liquid, and thus the system tends to preventcontamination of ground or air.

FIG. 2 shows a detailed cross section of a portion of the preferredembodiment of FIG. 1, in which a slurry 30 of solids 4 and liquids 6,e.g., sludge and water, is contained in a settling pond with an earthfloor 2 and is covered by a laminate or sandwich 8 of an aggregatematerial 32 contained between two layers of non-woven fabric 34 and 36.This laminate is covered by a heavy overburden of clay 20, whichprovides sufficient additional weight to press the laminate into theslurry 30. Liquid is thus filtered through the lower layer 34 ofnon-woven fabric and enters the aggregate layer 32, but the liquid isretained within the aggregate layer 32 by the top layer of fabric 36 andthe clay 20, which is impermeable to liquid. Liquid is extracted fromthe aggregate layer 32 by perforated tubes 10 with perforations 11 whichpass through this layer, or can be allowed to simply drain through theaggregate layer 32 to a sump or collector 18 along the edges of the pond(as shown in FIG. 1), where it is pumped out. More than one aggregatelayer can be provided as a laminate in combination with multiple layersof fabric. As liquid is removed from the aggregate layer 32, thelaminate is pushed further into the slurry 30, and finally will restatop a nearly liquid-free layer of separated solids 4. For maximumeffectiveness, the edges of the laminate material should reach oroverlap the edges 5 of the settling pond and should be anchored tosideboards or the like which line the circumference of the pond. Oncethe liquids have been separated and removed, the laminate material canbe left in place on top of the de-watered sludge and fill dirt can beplaced theron for land recovery purposes. Alternatively, means can beprovided for the temporary removal of the laminate material so that moreslurry materials may be dumped into the pond and the process repeated.Dependent upon the size of the pond, the density and viscosity of theslurry and other factors, it may be desirable to provide mechanicalsupport or means for exerting pressure on the top of the layer.

FIG. 3 shows a simpler preferred embodiment which may be preferable whenadditional slurry material is to be added periodically to the settlingpond. A layer of non-woven fabric 40 is placed atop the slurry or sludgematerials 30 in a settling pond, and is weighted down by a series ofdiscrete or relatively continuous and water-permeable weights, e.g., amixture of aggregate and larger stones 42. Optionally, mechanical meansof support or weighting can be provided, such as frames, grates, barsand the like, similar to frame and wire mesh shown in FIG. 5. Perforatedtubes 10 are passed along the top of the non-woven fabric 40 so that theliquid can be pumped off as it is separated and filtered through thefabric 40. Such tubes may be permanent, semi-permanent or inserted onlyfor removing the liquid on specific occasions. They are preferably madeof rigid, semi-rigid or flexible plastics such as polyvinyl chloride,polypropylene or polyethylene. The perforations should be of a size andspacing such that liquid can be effectively pumped or drained from thetubes without clogging the perforations. This embodiment can be arrangedso that the fabric can be physically removed periodically from thesurface of the pond, allowing new slurry or sludge materials to be addedto the pond. For instance, the non-woven fabric can be mounted in aframe 101 or supported by mechanical means such as mesh, grates or bars102 of suitable materials as shown in FIG. 5, which is discussed in moredetail below. For instance, if a frame of suitable rigidity for theweight of the damp fabric is provided it could be hoisted from one ormore sides to allow additional slurries to be added. Also, if lateralweighting and stiffening bars were provided for a layer of such fabric,the fabric could be stored upon a roller and unrolled across the pond asif using a window shade, then secured to the opposite side of the pondwhen in use. To store the fabric on a roller in such manner, it may berequired to scrape off accumulated sludge as the fabric is rolled up.

Numerous alternative embodiments can be provided, utilizing theprinciple of forcing at least one layer of, e.g., liquid-permeablefabric into a slurry or mixture of solids and liquids so that the liquidis separated and can then be removed, leaving the separated solids belowthe fabric.

In FIG. 4, a plurality of liquid extraction tubes 10 are spaced acrossthe width of the laminate and are connected to a common removal sump 18.In this variation of the embodiment, the non-woven layers 34 and 36 arenot in liquid contact with sump 18, but simply enclose the aggregatelayer 32. Said sump 18 can also be made of rigid, semi-rigid, orflexible plastic such as polyvinyl chloride, polypropylene orpolyethylene.

Also a more detailed view of the layers is shown. An earthen floor 2having slurry 30 composed of liquid 6 and solids 4 thereon is covered bya non-woven fabric layer 34. An aggregate layer 32 surrounds the liquidremoval tubes 10 and sump 18, with a second non-woven layer 36 spacedbetween said aggregate layer 32 and clay cover sealing layer 20.

In FIG. 5 a reuseable filtering means allowing slurry to be added and/ordried sludge to be removed from a settling pond or fill area is given. Anon-woven filter material 100, such as the embodiment of the inventionshown in FIG. 3, is supported within metal frame 101 (preferablyaluminum tube) by means of mesh 102 (such as galvanized wire mesh) overa sludge containing area with walls 115. Said frame 101 and wire mesh102 are so constructed as to present a rigid integral structure 103.Said structure 103 is supported along side 104 by pivotal ringattachments 105 which allow for rotation of tube 106 within said rings105. The opposing side 107 of structure 103 has lifting means 108attached along the length thereof for both maintaining said structure103 while in the horizontal filtering position and in the verticalraised position. Lifting means 108 preferably comprise tempered steelwire capable of withstanding at least as much tension as is generatedwhile lifting. Lifting wires 108 are routed through fixed pulleys 109mounted atop poles 110 and extend to motorized windlass means not shown.

In addition, the structure 103 pivotal support means 105 are slideablyattached by ring members 111 through bar means 112 to vertical rigidpoles 110. Said poles 110 (preferably telephone type poles) are the mainsupporting means for structure 103 and extend to a height sufficient toallow said frame 101 to be raised almost vertical. The slideable rings111 are moveable vertically along poles 110 by motor means not shown andcan be secured in place by clamps, pins or other conventional means notshown. The poles 110 and rings 111 are placed so that structure 103 canbe lowered into contact with the surface of the sludge.

In completion of the invention, liquid removal means 113 extend acrossthe surface of filter mat 100 and connect to manifold tube 114 which isconnected to a disposal reservoir and pumping means not shown. Saidliquid removal means 113 are preferably perforated tubes closed at theend opposite manifold tube 114 and attached to frame members 106 and 107by conventional mechanical means 116 and 120 to prevent excessiveflexing or sagging.

In operation, the non-woven fabric, wire mesh, metal frame structure 103is raised almost vertical. Saturated sludge is placed within the sludgecontainment area walls 115 and the structure 103 is lowered to ahorizontal position. Then motor means not shown are operated to lowerstructure 103 down poles 110 into contact with the surface of saidsludge. Liquid is filtered through mat 100 into fluid contact with tubes113. Tubes 113 then are used to remove the filtered liquid throughmanifold 114 by pumping or draining. After deliquefaction, additionalsludge can be added and/or the dried sludge removed by raising andpivoting the filter structure 103 as described above. The sludgecontainment area can be a small area, substantially covered by thefilter structure 103, or can merely be a small portion, preferably acorner, of a much larger sludge area which is otherwise covered byfilter means such as other embodiments of this invention. In the lattercase, this permits the addition of wet sludge and/or the removal ofdeliquefied sludge without disturbing the layers of filter materialwhich substantially cover the remainder of the sludge area. Thus, theentire surface of the sludge need not be exposed, reducing losses ofliquid by evaporation, contamination of the atmosphere, etc.

Many types of fabrics can be used as the liquid-permeable fabrics ofthis invention, e.g., woven, non-woven or felted fabrics, with sometypes preferred for particular applications. For example, the fabricmust not be dissolved, oxidized or weakened significantly by theliquid-solid slurry with which it comes in contact, at least during theconsolidation period, but where the filtering means are to be left inplace as part of a landfill, it can be advantageous to use fabricscomprising biodegradable fibers of natural or synthetic materials. Thus,fabrics useful in this invention can comprise fibers of natural,synthetic or processed inorganic materials, e.g., jute, hemp, polymers,fiberglass, metals, carbon, asbestos, etc. Tests have shown that certainnonwoven fabrics display excellent characteristics for suchapplications, including good hydraulic conductivity, non-clogging, lowcost, availability and ease of handling. Furthermore, such nonwovenfabrics are very effective in reducing color and turbidity in a filteredliquid. See, e.g., U.S. Pat. No. 4,222,877, column 1. Certain of thesenon-woven fabrics also provide good tensile strength and are availablein large sheets or rolls which facilitate their use in large scalesettling ponds or the like. Advantages of this invention include thefaster dewatering of such settling ponds and the reduction in thesurface area required for the disposal of a given amount of slurry ofsolids containing solids and liquids.

The most preferred materials for use as such liquid-permeable fabricsare presently the non-woven polypropylene fabrics comprising needlepunched, staple fibers, fused on one side, unfused, fused on both sidesor double fused on one side, produced and marketed by the PhillipsFibers Corporation as Petromat®, Duon®, or Supac®. These fabrics displayexcellent filtration characteristics, as described more fully herein,will not rot and are not attacked by most chemicals. Since the fabrichas random fiber orientation, it offers desirable multi-directionalproperties of elongation and tensile strength and resists tears orpunctures. This fabric is conventionally marketed in rolls, in widths upto 15 feet and lengths of up to 300 feet, and can be fabricated to orderin desirable widths and lengths. Sections of such fabric can be joinedin a seam by sewing using, e.g., a portable air-operated sewing machine.

Since commercial polypropylene fibers are wettable and wick rapidly dueto the presence of hydrophilic lubricants on the surface of the fibers,these fabrics provide the advantage of wicking liquids from a slurrywith which they are placed in contact onto the "liquid side" fordraining or pumping. Other wettable fibers, natural or synthetic, arealso useful in this respect. Examples include acrylic and rayon fibers.

In operation, the liquid-permeable fabrics of this invention are forcedor pressed so as to descend into the slurry by gravity or other means sothat the liquid passes up through said fabric with the solids remainingbelow; the liquids can then be removed from above the fabric. Althoughwater is the most common waste liquid encountered in the industriesmentioned above, this invention is also applicable to the separation ofsolids from oils, organic or inorganic liquids, liquid chemicals, andacids or mixtures thereof with water, so long as the liquids involvedare compatible with the fibers of the fabric material. (For instance,some asbestos materials are soluble in acids, and polypropylene can bedissolved by chemicals including chlorinated hydrocarbons comprisingperchloroethylene, hot mineral oil, xylene and decalin.)

The ability of the preferred fabrics of this invention to reduce colorand turbidity in the filtrate liquid is of particular advantage indewatering slurries of environmentally offensive wastes.

Since some of these liquids have greater effect on the synthetic fibersof such fabric materials when heated, the separation processes of thisinvention are preferably carried out at ambient temperature. However,such processes can be carried out at temperatures below the softeningtemperature of, e.g., the polypropylene fibers, provided the operatingtemperature is below the boiling point of the liquids involved.

The solid material separated from such liquids can be particulate,granular, gelled or flocculated materials, crystals, dusts, sludge, orgels such as for example sand, sulfur particles, carbon black, clays andthe like. The liquid-permeable fabrics of this invention can besupported and/or pressed down upon the slurries by mechanical meanscomprising grates, bars, frames, sideboards, overburdens ofwater-permeable weighting materials such as gravel or aggregates, orwater-impermeable overburdens such as clay. Once the liquids have passedthrough said fabric the liquids can be removed by any suitable means,such as for example by draining, pumping, absorbing, evaporating and thelike. When this invention is practiced in vessels for industrial orlaboratory use, liquids can also be removed by decanting, vacuumdistillation or other suitable means known in the art. Some embodimentsof the water-permeable weighting means can include aggregates comprisinggravel of pea size or larger, crushed concrete, spent oil shale, smelterslag, etc.

Where it is desirable to separate and remove the liquids from a slurrywithout allowing the surface of the separated liquid to be exposed tothe atmosphere, a top overburden layer can be provided of a clay such asbentonite, a montmorillonite clay which absorbs water or small polarorganic molecules, then swells and becomes impermeable to liquids. Thisis of particular advantage where it is important to remove or recoverall the liquid from the slurry, rather than allowing it to escape andcontaminate the surrounding ground or atmosphere.

ILLUSTRATIVE EMBODIMENT

Although the following embodiment has not been constructed, appropriatedetails are provided to further illustrate how the invention can bepracticed.

A hypothetical sludge pond has the dimensions of 200' wide by 280' longtotaling a 56,000 sq. ft. effective surface area. Said pond is coveredby 5 oz. per sq. yd., lightly fused on one side, nonwoven polypropylenefabric such as Supac®, sold by Phillips Fibers Corporation ofGreenville, SC. The fabric cover is constructed from twenty-two 10' wideby 300' long sections sewn together by an air operated sewing machineand overlapping 1" at the seams for a total effective surface area of(218'3" by 300') 65,475 sq. ft. The fabric extends 9'11/2" onto the soilat pond edge in the width direction and 10' onto the soil at pond's edgein the length direction. Said material has a rupture strength minimum of295 lbs. per sq. inch over the fabric body and approximately 265.5 lbs.per sq. inch over the seams. The fabric is 70 mils (0.07") thick and hasa water permeability rate of 0.086" per sec. Said fabric is covered bygravel or conglomerate concrete to the thickness of 4", having a weightof 0.348 lbs. per sq. inch at that thickness. The gravel or concretelayer is covered by a second layer of the same 5 oz. fabric which iscovered by 10" of Bentonite clay weighing 0.63 lb. per sq. inch at thatthickness, comprising 10% water by weight. Based on the permeabilityrate found using ASTM 751 and the effective surface area of 8,064,000square inches, the total effective filtration rate over the surface ofthe fabric is 3064 gal. of water per sec. Also based on the sum of theindividual weights, the total amount of weight pushing on the fabric persq. inch is about 1 lb. per sq. inch, including the clay and theaggregate. The water filtrate is removed from above the pond by aplurality of perforated polyethylene tubes or pipes such as are soldunder the trademark Driscopipe® by Driscopipe, Inc. of Dallas, Tex.Pipes of a diameter in the range from about 0.5 to about 1.5 inches aresuitable, and perforations of about 0.1 to about 0.3 inches can bespaced so that there are from 10 to 30 perforation per foot, distributedrandomly or symmetrically around the periphery of the tubes. Said pipescan be manifolded into a common drain or sump along one edge of the pondand the water pumped away.

A UV stabilized nonwoven polypropylene fabric suitable for the practiceof this invention, marketed by Phillips Fibers Corp. as Petromat®, hasthe following relevant properties:

    ______________________________________                                        Fiber Specific Gravity                                                                        0.90-0.91                                                     Effect of Heat  Fiber softens at 300°-320° F.,                                  melts at 320° F.-340° F.                        Flammability    Classed as very slow burning.                                 Effect of Solvents                                                                            Some chlorinated hydrocarbons                                                 cause slight swelling at room                                                 temperature and dissolve poly-                                                propylene at 160° F. or above.                                         Fiber is insoluble in aliphatic                                               alcohols, glycerine, ether, carbon                                            disulfide, acetone, trichloroethane,                                          trichloroethylene and methylene                                               chloride. Hot perchloroethylene,                                              mineral oil, xylene (140° C.) or                                       decalin (100+° C.) will dissolve                                       polypropylene. UV stabilization                                               prevents the fabric from weakening                                            due to outdoor exposure.                                      ______________________________________                                    

For a thickness of 40-100 mils, to be specified, properties are asfollows:

    ______________________________________                                        Weight, oz./sq. yd.                                                                              About 4-6                                                  Tensile strength, lbs                                                                            90 to about 115 nominal                                    (ASTM D1682) min                                                              Elongation at break, %                                                                           55 to 65                                                   (ASTM D1682)                                                                  Burst strength (Mullen)                                                                          350 lb./sq. in. (90% of                                    ASTM 751           this for sewn seams)                                       ______________________________________                                    

While it is not intended to limit the invention by such description,examples of such settling ponds can cover 1 to 15 acres at 4 to 25 feetdepth, and take 1 month to a year or more to de-water.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby, but it isintended to cover all the changes and modifications within the spiritand scope thereof.

I claim:
 1. A method for dewatering a slurry of solids and liquid havinga surface contained in a settling pond and for covering the solids ofsaid slurry so as to form a landfill, comprising the steps of:(a)placing atop the surface of said slurry of solids and liquid containedin said settling pond at least one layer of non-woven liquid-permeablefabric having a top surface and a bottom surface and adding at least onelayer of liquid-permeable weighting means selected from the groupconsisting of gravel, crushed concrete, spent oil shale and smelter slagonto said fabric to create a negative buoyancy, such that said fabricsinks into said slurry in response to said negative buoyancy created bysaid liquid-permeable weighting means to cover and confine said solidsand thereby causes at least a portion of said liquid to pass throughsaid at least one layer of non-woven liquid-permeable fabric for removalfrom said slurry; (b) removing said at least a portion of said liquidwhich is caused to pass through said at least one layer of non-wovenliquid-permeable fabric from said settling pond by pumping, draining orevaporation, utilizing said at least one layer of non-wovenliquid-permeable fabric and said at least one layer of saidliquid-permeable weighting means as drainage channel means for removingsaid at least a portion of said liquid; and (c) covering said at leastone layer of non-woven liquid-permeable fabric, said liquid-permeableweighting means, and said solids with materials selected from the groupconsisting of clay, earth, sand, aggregates and vegetable matter to forma landfill.
 2. A method in accordance with claim 1 wherein said liquidis selected from the group consisting of water, oils, organic liquids,acids, and mixtures thereof, which are compatible with saidliquid-permeable fabric.
 3. A method in accordance with claim 1characterized further as including adding a layer of liquid-permeableclay onto the materials of step (c) as a fluid-retentive top layer.
 4. Amethod in accordance with claim 1 wherein said liquid-permeable fabricis a non-woven synthetic or inorganic fabric.
 5. A method in accordancewith claim 1 wherein said liquid-permeable fabric is a non-wovensynthetic fabric comprising needle punched staple fibers ofpolypropylene fused on at least one side.
 6. A method in accordance withclaim 5 wherein said non-woven synthetic fabric has random fiberorientation.
 7. A method in accordance with claim 1 wherein saidliquid-permeable fabric comprises natural or synthetic fibers which arebiodegradable.
 8. A method in accordance with claim 1 further includingthe step of anchoring said liquid-permeable fabric to sideboards.
 9. Amethod for separating liquid from a slurry of solids and liquidscontained in a settling pond having a surface, comprising:(a) placingatop the surface of said slurry contained in said settling pond alaminate comprising at least one layer of non-woven liquid-permeablefabric and at least one layer of materials selected from the groupconsisting of gravel, crushed concrete, spent oil shale and smelter slagon said at least one layer of non-woven liquid-permeable fabric asliquid-permeable weighting means and drainage channel means, each layerof said laminate having a top surface and a bottom surface; (b) allowingsaid laminate to at least partially sink into said slurry in response tosaid liquid-permeable weighting means, so that said solids are coveredand confined below the bottom surface of a lowest layer of said fabricin said laminate and at least a portion of said liquid passes from belowthe bottom surface of said lowest layer of said fabric into said atleast on layer of materials; and (c) removing at least a portion of saidliquid from said at least one layer of materials.
 10. A method fordewatering a slurry of solids and liquid having a surface contained in asettling pond and for covering the solids of said slurry so as to form alandfill, comprising the steps of:(a) placing atop the surface of saidslurry of solids and liquid contained in said settling pond a laminatecomprising at least one layer of non-woven liquid-permeable fabriccomprising synthetic or inorganic fibers and at least one layer ofmaterials selected from the group consisting of gravel, crushedconcrete, spent oil shale and smelter slag as liquid-permeable weightingmeans and drainage channel means, such that said laminate sinks intosaid slurry in response to said liquid-permeable weighting means andthereby causes at least a portion of said liquid to pass through said atleast one layer of said liquid-permeable fabric into said at least onelayer of materials for removal from said slurry; (b) removing said atleast a portion of said liquid from said settling pond by pumping,draining or evaporation through said at least one layer of materials;(c) covering said laminate and said solids covered thereby with a layerof liquid-permeable clay, followed by at least layer of additionalmaterial selected from the group consisting of clay, earth, sand,aggregates and vegetable matter to form a landfill.